The present invention relates to an electric compressor having an electric motor and a compression mechanism accommodated in a housing.
Conventionally, electric compressors have been used as compressors for vehicle air conditioners. Such an electric compressor includes an electric motor and a compression mechanism that are integrated (for example, refer to Japanese Laid-Open Patent Publication Nos. 2004-100683 and 2004-112988). FIG. 6 is a cross-sectional view showing such an electric compressor 30. As shown in FIG. 6, the electric compressor 30 has a compressor housing 31 forming an outer wall of the compressor 30. The compressor housing 31 includes a first housing member 31a and a second housing member 31b. The first housing member 31a and the second housing member 31b are secured to each other by fasteners 32, so that a sealed space 33 is defined in the compressor housing 31. A rotary shaft 34, which is rotatably supported by the first housing member 31a, is accommodated in the sealed space 33. An electric motor 35 and a compression mechanism 36 are also accommodated in the sealed space 33. In FIG. 6, a dashed line labeled with a letter L represents a central axis of the rotary shaft 34 (a central axis of the electric compressor 30). The electric motor 35 has a stator 35a and a rotor 35b, which is surrounded by the stator 35a and fixed to the rotary 30 shaft 34. The compression mechanism 36 is a scroll type compression mechanism having a fixed scroll 36a and a movable scroll 36b. 
When the compression mechanism 36 is actuated by the 35 electric motor 35, low-temperature and low-pressure refrigerant gas is supplied to the sealed space 33 from an external refrigerant circuit (not shown) via an inlet (not shown) formed in the first housing member 31a. The refrigerant gas is then drawn into the compression mechanism 36 through the electric motor 35. The refrigerant gas drawn into the compression mechanism 36 is compressed by the compression mechanism 36, and becomes high-temperature and high-pressure refrigerant gas. Then, the refrigerant gas is discharged to the external refrigerant circuit (not shown) through an outlet 37 formed in the second housing member 31b. Since the refrigerant gas is guided to the compression mechanism 36 from the external refrigerant circuit through the electric motor 35, the refrigerant gas serves to cool the electric motor 35.
In the above described electric compressor 30, the annular stator 35a is fitted to the compressor housing 31, specifically, to the first housing member 31a, by shrink fitting or press fitting.
To reduce the weight of the electric compressor 30, for example, the thickness of the compressor housing 31 may be reduced. However, reduction of the thickness of the compressor housing 31 is not easy for the following reasons. That is, when the temperature and pressure in the compressor housing 31 are increased due to an increase in the ambient temperature (for example, the temperature in the vehicle engine compartment), the compressor housing 31 is deformed due to the pressure difference between the inside and the outside of the compressor housing 31. Thus, if the compressor housing 31 is made excessively thin, there is a possibility that the electric motor 35 (the stator 35a) cannot be firmly fixed to the housing 31. For example, if the amount of deformation of the compressor housing 31 exceeds the amount of interference of the stator 35a, the stator 35a cannot be firmly fixed to the housing 31. Particularly, if the compressor housing 31 is made of aluminum in view of reduction of the weight, the influence of deformation becomes noticeable. Therefore, the thickness of the compressor housing 31 needs to be determined such that, a sufficient interference for maintaining the fixation of the electric motor 35 (the stator 35a) remains even if the compressor housing 31 is deformed.